1. Field of the Invention
The present invention relates to a projection apparatus, and more particularly, to a projection apparatus having a projection lens with two-time image formation.
2. Description of the Prior Art
To project an image at a big space such as a big conference room or a hall, a bigger projection image is required so that the observer can clearly see the image. However, the size of the projection image of the projection apparatus is subject to the structural design of the projection lens. Thus, a wide-angle projection lens is commonly used in the projection apparatus. Conventionally, the design of the wide-angle projection lens is based on a technology of one-time image formation, which would normally lead to the problems such as the front lens group being too big so as to increase the manufacturing cost and difficulty for manufacturing the projection lens. Accordingly, a projection lens utilizing a mirror disposed off an optical axis or a projection lens having a lens with a specific lens surface has been developed to shorten a projection distance. However, the projection lens utilizing a mirror disposed off an optical axis has more instability, and the size of the mirror is too large so that difficulty for manufacturing the projection lens is increased, and the projection lens is not easily accepted in this field.